Lasers are recently making a remarkable progress. Particularly, as for the solid laser, semiconductor laser and gas laser of emitting ultraviolet light, visible light or infrared light at a wavelength of 300 to 1,200 nm, high-output compact lasers are easily available and these lasers are very useful as a recording light source in lithographic printing of directly producing a printing plate based on digital data of a computer or the like. Various studies are being made on the recording material sensitive to these various laser rays and, for example, a positive recording material for use with an infrared laser having a sensitive wavelength of 760 nm or more (see, U.S. Pat. No. 4,708,925) and an acid catalyst crosslinking-type negative recording material (see, JP-A-8-276558 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)) are known. Also, radical polymerization-type negative recording materials for use with an ultraviolet or visible laser at 300 to 700 nm are known (see, U.S. Pat. No. 2,850,445 and JP-B44-20189 (the term “JP-B” as used herein means an “examined Japanese patent publication”)).
Such a negative image recording material usually contains a compound capable of generating a radical under light or heat (hereinafter sometimes referred to as a “radical initiator”) and a compound having an ethylenically unsaturated bond (hereinafter sometimes referred to as a “polymerizable compound”), and utilizes a recording system of bringing about a polymerization reaction of the polymerizable compound by using a radical generated under light or heat as the initiator. Particularly, a lithographic printing plate precursor comprising a hydrophilic support having provided thereon a photopolymerization-type recording layer having excellent photosensitization speed and containing a radical initiator, a polymerizable compound and a binder polymer soluble in an alkali developer has advantageous features such as excellent productivity, simple and easy development processing, high resolution and good inking property and therefore, can give a printing plate having desired printing performances.
With respect to the binder polymer soluble in an alkali developer, for example, an acrylic binder polymer such as acrylic acid copolymer and methacrylic acid copolymer is generally used, but use of various binder polymers is being studied for the purpose of more enhancing the performance.